Recent advances in technology have made more appealing the widespread use of electronic thermometers to measure temperature, especially in the medical field. Typically such systems include a thermometer unit and a temperature sensing probe unit which may be used with disposable covers. These systems are initially relatively expensive compared to mercury thermometers but over their useful life they cost considerably less to use and are less consuming of the time of scarce and expensive medical personnel. However, since these thermometers are electronic they require electrical power for their operation which is supplied in the form of batteries to promote the portability of the electronic thermometer systems. The system requires substantial electrical power to operate the sensing and measuring circuits and to operate the display; as a result the batteries may be relatively quite large and heavy in order to provide sufficient power for operating the system over a reasonable period of time. Periodically the batteries are removed and replaced with new ones at additional cost or the system is removed from service while the batteries are recharged. Poorer battery duty cycles result if the user habitually unnecessarily extends the measuring and display period or inadvertantly fails to switch off the system at the end of its use.